After 4 years of drilling and reading Rh levels once or twice a year for our company, I just learned yesterday, because of concerns on my part for consistently getting high readings, and from viewing this website, of the 40/20 depth requirement for proper readings. Yeah WOW! - That's what I said.
My training consisted of verbal instruction from a co-worker who had performed tests initially, and is no longer with the company, to reading the directions that came with the early readers. "Drill your holes 1 3/4 - 2" deep", he said.
From what I have learned in the last two days of research, on my own time and of my own initiative, is that I have been doing the tests correctly in every step, except for this one.
Now my superiors at my company are blaming me for not doing the tests correctly. Even though I was never given adequate instruction, I feel my job is in jeopardy. I do tests when asked to (infrequently), and I'm an installer (35 years experience, 17yrs. w/ company) primarily. This lapse has cost us a lot of money, not to mention unreliable results. Since I am not certified, and our company, not wanting to be held legally responsible for giving a go ahead for installation after high readings, another testing company is being brought in to verify our results. More time and money spent!
I want to be proficient at testing, and feel I am close, thanks to the information I have gained here. I will plead my case to my superiors for more education/knowledge/certification and see what happens. You guys really are Concrete Gurus!
Now to my question: having drilled holes 2" deep in a slab that is 3" thick, poured over a corrugated pan appox. 1/8" thick (according to some field measurements taken), what would the correct depth of holes be for the probes? .6" or 1.2" 20% or 40%? Also, if drilling .6", won't the probes stick out 1" above the slab? Is this normal, and how do you prevent them from damage from lifts, bakers, etc.?
I need to know where I made my mistake,for my own piece of mind, so hopefully, this will not occur ever again.

1) Having a copy of the ASTM F2170 standard for which the Rapid RH was designed to meet, is a must. Have you ever been given one? I find the answer to this to be no more times than not when I talk to people. This should not be on you.

2) I have a hard time believing that the pour on this pan is this shallow. Usually the shallow part would be around this deep but not the deep section of the pan. With that being said, alot of people will cut the top of the barrel off on shallow pours such as gypsum where it is being used for soundproofing.

3) Determining whether 20% or 40%-Is the slab drying from one or two sides? Any pan decking on the market, even "vented" decking, is only drying from one side, thus 40% is required. The easiest way to determine whether the slab is open on the bottom is go to the lower level and look up. Can you see concrete or corrugated metal?

Jason: THANK YOU! answer to 1) - no ; 3) -corrugated
Knowledge is King and I will download ASTM F2170 and study it. Will call personnel on job site and have him double-check thickness, he has told me it was 3-3 1/4". Will see if a core drilling is still available to verify.
I know this isn't rocket science, but it certainly is Concrete Science!! Much to know and so many variables. With so much time and money riding on proper readings, decisions on whether moisture mitigation is needed or not, one had better educate oneself on all aspects of this area. This I will undertake, once again, of my own volition, hopefully with company support, for their best interest. I don't think it would be wise for them to turn this responsibility over to some other poor smuck and end up with the same results.
Thanks again

One more question: When using the 3/4" drill bit w/the small pilot drill on the end, what is the proper depth measurement for probe holes? From the tip of the small pilot drill, or the end of the 3/4" main drill body?

You still have the old probes with the narrow point on the end? The ones that were self contained and didn't have a separate reader?

Does your probe look like the attached picture? With those old probes we measured to the tip of the drill bit.

The correct procedure for slabs on a pan is to measure the deepest part of the pan (bottom of flute) and drill to 40% at that point. If the pan were a maximum depth of 3", you'd drill 1.2" down over the deep flute.

What I like to do is find a plumber's or electrician's core and then measure right there, and place my probe about 2 feet away from the core hole. This way I know the depth of the concrete (it can vary several inches on a pan as the pan sags while placing concrete!) and I will know the location of the flutes.

That's all interesting- I've often wondered about how you know the exact slab thickness, therefore how you know whether you are conforming exactly to F2170. Would some go so far as to core at every probe location?

The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

I've found more often than not on a renovation project, no one knows, or will take the time to find records of slab depths, and you have to place the sensors NOW.

I keep a 12" length of coat hanger with a pre-formed hook at the end in my tool case. I trill a 3/8" hole all the way thru the slab (after determining there is now rebar there with my Bosch sensor), push the wire thru, pull up til the hook catches and you have your depth. Obviously slab depths can vary, so it's up to you and the GC or Flooring Installer how many areas you drill thru and it adds time to your testing costs. So, I just establish a cost per hole and let them make the call. Just make sure you document everything agreed to in your report

It seems that this topic is only directed to an above level concrete slab w/pan? It is somewhat silly to even do an RH reading of this type slab. Moisture levels in these above level cement poured substrates will continently fluxuate to unknown severities depending on what is happening environmentally below. To try to find a liquid application of a vapor barrier, based on the maximum tolerances of any product is ludicrous. All above crete type slabs must be sealed with a barrier which should meet or exceed the permeation rating of the 6mil plastic sheet. That of lesser perm value is rather a gamble in any sense.
YT,
GP-CA